In optical communication using optical fiber, optical modules have been used that have light emitting elements for transmission or reception. An optical module has an optical receptacle that optically couples light emitting elements or light receiving elements and the end faces of optical fibers. In the optical module at a transmission side, the optical receptacle causes light (hereinafter, called “signal light”) that includes communication information and is emitted from the light emitting elements to be incident on the end faces of the optical fibers. In the optical module at a reception side, the optical receptacle guides the signal light emitted from the end faces of the optical fibers to the light receiving elements. The optical receptacle that collectively couples a plurality of light emitting elements or light receiving elements and the end faces of a plurality of optical fibers has a plurality of lens faces arranged at predetermined pitches, and therefore, may be called a lens array.
Some of the optical modules at the transmission side have light receiving elements for monitoring output of the light emitted from light emitting elements, in addition to the light emitting elements. The optical receptacle for use in such a light module is configured to emit a part of the light emitted from the light emitting elements toward the light receiving elements for monitoring as monitor light (see PTL 1, for example).
FIG. 1A is a sectional view of the lens array described in PTL 1. As illustrated in FIG. 1A, lens array 10 described in PTL 1 includes lens array main body 20, lens member 30 and filler 40. Lens array main body 20 and lens member 30 are formed of resin with optical transparency. Filler 40 is an adhesive with optical transparency having the same refractive index as the resin composing lens array main body 20. In lens array main body 20, a plurality of first lens faces 21, first reflection surface 22, second reflection surface 23, half-mirror layer 24, and a plurality of second lens faces 25 are formed. In the bottom of lens array main body 20, recess 26 is formed that is to be filled with filler 40 and that is for lens member 30 to be inserted therein. On an inclining surface located at the bottom of recess 26, a dielectric multilayer film is formed as half-mirror layer 24. Lens member 30 is inserted into recess 26, and has a plurality of third lens faces 31. Filler 40 fills a space formed between half-mirror layer 24 and lens member 30, and bonds lens array main body 20 and lens member 30 together.
FIG. 1B is a sectional view (a view of an optical path) of the optical module at the transmission side described in PTL 1. In this drawing, hatching onto a section of lens array 10 is not illustrated for the purpose of better illustrating the optical paths. As illustrated in FIG. 1B, optical module 50 at the transmission side has optoelectric converting device 60 for transmission, and lens array 10 illustrated in FIG. 1A. To a front face of lens array 10 (a face located at the left side in FIG. 1B), a plurality of optical fibers 70 are connected. Optoelectric converting device 60 for transmission has substrate 61, a plurality of light emitting elements 62, a plurality of light receiving elements 63 for monitoring and a plurality of control sections 64. A plurality of light emitting elements 62 are linearly arranged on substrate 61. A plurality of light receiving elements 63 are linearly arranged on the same surface of substrate 61 to be parallel with the line of light emitting elements 62. A plurality of light emitting elements 62 face corresponding first lens faces 21 of lens array 10. A plurality of light receiving elements 63 face corresponding third lens faces 31. A plurality of control sections 64 are linearly arranged on the same surface of substrate 61 so as to be located between light emitting elements 62 and light receiving elements 63. Control section 64 is connected to light emitting element 62 and light receiving element 63, and controls output of light emitting element 62 based on intensity or an amount of light of monitor light Lm that is received by light receiving element 63.
As illustrated in FIG. 1B, light L emitted from light emitting element 62 enters lens array 10 from first lens face 21, is sequentially reflected on first reflection surface 22 and second reflection surface 23, and reaches half-mirror layer 24. On half-mirror layer 24, a part of light L passes through half-mirror layer 24 to be monitor light Lm, and a part of light L is reflected to be signal light Ls. Monitor light Lm sequentially passes through filler 40 and lens member 30, is emitted to outside lens array 10 from third lens face 31, and reaches light receiving element 63. Signal light Ls is emitted to the outside of lens array 10 from second lens face 25 to reach an end face of optical fiber 70.
As described above, lens array 10 described in PTL 1 can split light L emitted from light emitting element 62 into monitor light Lm and signal light Ls, and emit monitor light Lm toward light receiving element 63, by using half-mirror layer 24. In lens array 10, recess 26 is filled with filler 40 with the same refractive index as that of lens array main body 20 so that light L is not totally reflected on half-mirror layer 24. In order to guide monitor light Lm to light receiving element 63 properly, lens member 30 is disposed in recess 26.